The goal of this proposed program is to design and fabricate novel nondiffracting transducers for high resolution and large depth of field pulse-echo imaging with high imaging frame rate and for diffraction-free tissue characterization. Our approach to achieving these goals is to design the nondiffracting transducers of appropriate size, frequency and element number and fit them into a mechanical sector scanner. The transmitted nondiffracting beam will be of large depth of field and high resolution (small width of the center lobe of the beam). To reduce the sidelobes of the nondiffracting beam and increase imaging contrast while keeping high imaging frame rate, we will transmit with a nondiffracting beam and receive with dynamically focused Gaussian shading. For tissue characterization, nondiffracting shading in both transmitting and receiving is required. Backscattering coefficient and slope of frequency dependent attenuation will be measured using nondiffracting beam transducers. Simplified algorithms (not requiring beam diffraction correction) will be developed for real-time tissue characterization. Imaging and estimation of tissue parameters will be tested quantitatively in vitro on phantoms and tissue samples and evaluated qualitatively in vivo with visual judgment by physicians. Nonsymmetric nondiffracting transducers will be designed and constructed so, that electrical beam steering and two-dimensional phased array scanning will be available. Successful implementation of this proposed program would contribute to advances in ultrasonic imaging and tissue characterization.